If you've moved SD to steem then exchanging it back is the same but opposite. If its on bittrex just transfer it to your wallet here and then use the internal exchange, use your... fuck it here watch these i made lol.

https://steemit.com/steem/@will-zewe/if-you-re-new-to-the-crypto-world-and-now-find-yourself-in-possession-of-a-few-steem-steem-dollars-take-a-watch-on-what-you-can